The present invention relates to a pattern fabrication method using a charged particle beam and an apparatus for realizing the same, and in particular it provides a pattern fabrication method and a device for realizing the same suitable for fabricating semiconductor integrated circuits having an extremely high degree of integration.
The circuit pattern for semiconductor integrated circuits has become finer and finer without interruption and tracing by using a charged particle beam having a high resolving power has been used for forming the fine pattern. Even by using a charged particle beam having a high resolving power, when the pattern becomes further finer, a phenomenon takes place that an interval between two parts close to each other in a large figure is further narrowed, which gives rise to a problem in the formation of fine patterns. This phenomenon is one of the most serious problems in the fine pattern exposure by means of a charged particle beam and it is known in general as the proximity effect. The cause of this phenomenon consists in that projected charged particles pass through a beam energy sensitive product (hereinbelow called resist) to enter a semiconductor substrate and that a part of charged particles scattered in the substrate, for example, returns again to the surface of the resist to expose it thereto. The effect of this reexposure is equivalent to a charged particle beam pattern faded in a large extent being projected again lightly thereon. As a result, since the exposure at a dense part in the pattern becomes an excessive exposure, this gives rise to the phenomenon that the interval is varied, as described above.
Heretofore, in order to reduce influences of this proximity effect, various contrivances have been made on the pattern to be exposed.
A first method therefor consists in that deformations in the pattern to be exposed due to the proximity effect are previously calculated and that modifications for compensating them are carried out previously on the pattern to be exposed. That is, since a small interval is further reduced in size by the proximity effect, as described previously, small interval parts are looked for previously in the exposure pattern data and the width of the figure is reduced by a suitable degree on both sides so that the small interval parts are enlarged. In this way, even if the small interval parts are further narrowed by the proximity effect, a figure having a desired size can be formed.
A second method therefor is a method by which the dose is varied at the exposure so that the proximity effect is compensated. As described previously, since the proximity effect is produced by the fact that a faded exposure pattern is reexposed, if the exposure is effected so that changing parts in the pattern are emphasized so as to compensate fading, a pattern similar to that obtained by performing a desired exposure can be formed as the result of the fading. For example, each of the figures are decomposed and only the contour portion is taken out, which is exposed for a longer time than the central portion. In this way, a pattern is exposed in which the high frequency component of the exposure pattern is emphasized, which cancels the effect of the low frequency component emphasis due to the fading, and exposure by which influences of the proximity effect are reduced in some degree can be effected.
Further, as a third method, there is known a method by which the irradiation dose with the charged particle beam is varied depending on the exposed area ratio per unit area, i.e. pattern density. Since the proximity effect is caused by excessive exposure, the irradiation time is shortened at the place where the exposed area ratio is high, and the irradiation time is lengthened at the place where the exposed area ratio is low. In order to execute this correcting method, an algorithm for a computer inputting data for the exposure in an electron beam exposure system is specifically designed. The idea of varying the exposure time depending on the exposed area ratio has been already disclosed also in JP-A 58-32420, 59-139625 and 61-284921 and thus it is known that this method is useful for correcting the proximity effect. Further refer to J. Vac. Sci. Technol. B3 (1), January/February, 1985, pp. 165-173, J. Vac. Sci. Technol. B7 (6), November/December, 1989, pp. 1524-1527, and J. Appl. Phys. 54 (6), June, 1983, pp. 3573-3581.
As described above, the proximity effect can be removed in the principle by pattern processing. However the number of exposure patterns for recent high density integrated circuits reaches such a tremendous value that it exceeds several millions in total. The processing of these patterns has reached an enormous amount and calculation for only one circuit pattern took from several tens to more than several hundreds of hours even with a super large scale computer. In addition, in the present situation, this calculation time increases rapidly with increasing degree of integration of the pattern and in realistic terms the execution thereof was difficult.